LTE (Long Term Evolution) is one of the wireless communication standards standardized by 3GPP (3rd Generation Partnership Project). In LTE, Single Carrier Access (SC-FDMA) is adopted as a wireless access scheme for an uplink. Further, in LTE, Orthogonal Frequency Multiple Access (OFDMA) is adopted as a wireless access scheme for a downlink.
A feature of OFDMA is that frequency orthogonality is used. In OFDMA, a plurality of carrier waves (sub carriers) are multiplexed. For this reason, it is said that the OFDMA scheme has better immunity to fading and multipath interference.
A feature of SC-FDMA is similar to that of OFDMA. The difference between SC-FDMA and OFDMA is that in SC-FDMA, a carrier wave assigned to a user is continuous. By this feature, in SC-FDMA, it is expected that the power efficiency of the uplink can be improved compared to OFDMA.
An uplink wireless resource provided in LTE is divided into two components: a frequency component and a time component. The divided wireless resource is assigned to the user.
A relay base station for LTE is specified in Non-patent document 1, non-patent document 2 and non-patent document 3. The relay base station is connected to a wireless base station by an Un link to configure a cell. In particular, among the wireless base stations, the wireless base station which accommodates the relay base station is called a Donner eNodeB (DeNB). The DeNB transfers data between a core network and the relay base station.
When a mobile terminal connected to the network moves from a connected cell to another cell, the mobile terminal changes the serving cell. This process is called handover.
At this time, in order to reduce the load on the mobile terminal and perform a handover at a high speed, a procedure in which a candidate of a handover destination cell is limited to a specific cell among the adjacent cells is generally used. Here, a list of the candidates for the handover destination cell is called an adjacent cell list.
A communication common carrier or an administrator of a network registers the cell for each cell to make the adjacent cell list. Further, the adjacent cell list is transmitted to the mobile terminal from the wireless base station which manages the cell via the downlink.
A priority of each cell is determined in the adjacent cell list. The priority shown in the adjacent cell list is generally determined based on the number of implementation times of the handover and a success rate of the handover. The priority of the adjacent cell is determined so that the adjacent cell of which the number of implementation times of the handover is large and the success rate of the handover is high may have higher priority. On the other hand, after the cell is added in the adjacent cell list, the cell of which the handover does not occur or the cell of which a failure of the handover tends to occur even when the number of implementation times of the handover is large is deleted from the adjacent cell list at the time of the next update of the list.
Further, the wireless base station monitors a load status of the cell. The load status is indicated by information about a usage rate of Physical Resource Block (PRB), the load on hardware, the load on a backhaul link, and information of the load on the whole wireless base station, or the like. In non-patent document 1, a method by which the adjacent wireless base stations transmit the information about the load status on each cell to each other is specified.
Further, the wireless base station collects a movement history of the mobile terminal. The movement history is included in a message that notifies of the handover. In non-patent document 1, a method for transmitting the movement history of the mobile terminal between the wireless base stations is specified. Specifically, the movement history is notified by UE (User Equipment) History Information included in Handover Request. This UE History Information can store information about the coverage area of the cell together with a cell ID. As a result, the wireless base station can obtain information about the coverage area of the surrounding cell.
The above-mentioned wireless network has been composed of mainly a macro wireless base station. Because the macro wireless base station has a large coverage area, the number of the wireless base stations installed by the communication common carrier has been small. However, in recent years, because the number of the mobile terminals which frequently connect to the Internet such as a smart phone and the like increases, many wireless base stations have to be installed. As a result, the number of the communication common carriers which plan to install a pico cell which has a small coverage area or the relay base station in addition to the macro wireless base station increases. As a result, because the number of the cells adjacent to one cell increases, it became difficult to make the adjacent cell list manually.
Further, as the related art, one example of a technology by which the cell of the wireless base station or the relay base station is set is described in patent document 1. In patent document 2, a technology by which an antenna angle is set so that the traffic between the cells may be dispersed is described.